The present invention relates to power management for a display. The invention further relates to but is not limited to power management for a display in a battery powered electronic device.
Conventionally, portable electronic devices such as cellular phones, portable digital assistants (PDA) or portable media players are equipped with battery or electrical power storage means for storing electrical charge to power to the electronic device when not connected to an alternating current (AC) or “mains” power source. Development of such portable devices has led to improvements in power management and efficiencies relating to transceiver processors, battery storage and displays. However a further design movement is to include larger display modules to enable a richer user experience. These larger displays generally consume or require more electrical power to operate than a smaller similar technology display module.
Furthermore the display module can be one of the largest power consuming components in any system. For example typical power consumption figures for a CMEL P0430WQLx-T 4.3″ 480×272 pixel display is in the order of 800 mW and a Densitron P0430WQLB 4.3″ 480×272 pixel display unit has a typical power consumption of 700 mW and a maximum power consumption of 950 mW. Power consumed in a display is typically directly proportional to the sum of the squares of the illumination of individual pixels. This is especially true for cathode ray tube (CRT), light emitting diodes (LED), organic light emitting diodes (OLED) and related display technologies. Conventionally to decrease the power requirement of a display module the brightness level of the entire display module is controlled. This can be seen, for example, in many portable computers which are configured to operate with a higher intensity back lighting or illumination when the device is connected to the mains power supply and a lower intensity when operating on battery or similar portable power supply. However this has the disadvantage that the visibility of the display module is adversely impacted at very low power levels, for example when displaying images with very low lit scenery or in bright sunlight where the image contrast is overwhelmed by the background light.